<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>案列</title>
  <style>
    .red{
      width: 100px;
      height: 100px;
      /*背景颜色*/
      background-color: red;
    }
    .green{
      width: 100px;
      height: 100px;
      background-color: green;
    }
  </style>
</head>
<body>
<div class="red"></div>
<div class="green"></div>
<div class="red"></div>
</body>
</html>